The present invention relates to the naturally occurring fungus, Valdensinia heterodoxa, and in particular to its use as a biocontrol agent for salal (Gaultheria shallon Pursh.).
Forest management has become increasingly intensive in order to maximize forest productivity and sustainability. The past few decades have seen significant changes in forest management practices, especially in the area of site preparation, the use of chemical herbicides, and development of new forest harvesting systems. Competition from non-commercial or competing forest vegetation is a major problem at conifer regeneration sites following harvest in plantations. This competition results in conifer mortality, reduced growth, delays in harvesting time, increased costs related to forest management, and decreases in annual allowable cut (Wall et al. 1992). Management of competing forest vegetation can take various forms, including removal by mechanical or manual brushing and chemical herbicides. These methods have distinct disadvantages such as non-target effects and public concerns about the negative impacts of using herbicides in pristine forest ecosystems. Hence, there is a growing need for alternative management strategies for competing vegetation that are cost-effective, environmentally safe, economically feasible, and sustainable (Watson and Wall 1995). One viable option is the use of naturally occurring plant pathogens as biological control agents which, if successful, are expected to result in increased early conifer growth rate and a shorter rotation age of commercially valuable crop trees (Shamoun 2000).
Salal (Gaultheria shallon Pursh.), a perennial, ericaceous shrub, is a serious competitor with conifer seedlings in coastal British Columbia. Generally, it competes with trees for water and nutrients and removal of salal leads to enhanced conifer growth (McDonald 1990). Salal is difficult to control with current mechanical methods due to its extensive root system leading to quick reestablishment through layering, sprouting, and suckering (D'Anjou 1990). Chemical herbicides are often ineffective since salal's thick and leathery leaves reduce herbicide translocation (D'Anjou 1990). Hence, salal can be considered a suitable target weed for biological control using fungal pathogens.
Numerous fungal species have been isolated from salal plants, including Mycosphaerella gaultheriae (Haeussler et al. 1990), Phyllosticta pyrolae Ellis et Everh. (Petrini et al. 1982), Phytophthora cinnamoni Rands (Lindermann & Zeitoun 1977), and Valdensinia heterodoxa Peyr. (Readhead 1974).
In 1999, a survey was conducted to collect and identify the mycobiota associated with salal from various locations on Vancouver Island (Shamoun et al. 2000).
Fungal pathogens isolated from diseased leaf and stem tissue were subsequently assessed for their virulence on salal. From the tested fungi, Valdensia heterodoxa (PFC 3027) caused substantial leaf damage on both detached leaves and intact salal plants (Vogelgsang et al. 2001).